With increasing industrial development, diverse electronic devices are used to achieve various purposes. An electronic device comprises a plurality of electronic components. Generally, different kinds of electronic components are operated by using different voltages.
As known, a power supply is essential for many electronic devices such as personal computers, industrial computers, servers, communication products or network products. Usually, the user may simply plug a power supply input cable into an AC wall outlet commonly found in most homes or offices so as to receive an AC voltage. The power supply will convert the AC voltage into a regulated DC output voltage for powering the electronic device. For example, the common DC output voltage is 12 volts. The regulated DC output voltage is transmitted to the electronic device through a power cable.
Generally, the magnitude of the output voltage is dependent on the electricity consumption of the system circuit. That is, the variation of the output voltage is very large. For reducing the variation of the output voltage, the power supply usually has an output voltage detecting circuit for detecting the output voltage and generating a detecting signal according to the output voltage. According to the detecting signal, the output voltage is adjusted so as to reduce the output voltage variation.
The power supply is connected to the system circuit through a power cable. When an output current flows through the conducting cable, a conducting voltage drop is generated by the power cable. Under this circumstance, the magnitude of the voltage across both terminal of the system circuit (i.e. a system circuit terminal voltage) is not equal to the magnitude of the output voltage. Although the use of the detecting circuit can reduce the output voltage variation, the system circuit terminal voltage is also changed as the electricity consumption of the system circuit. In other words, the variation of the system circuit terminal voltage is still very large. Since the gap between the system circuit terminal voltage at the maximum electricity consumption of the system circuit and the system circuit terminal voltage at the minimum electricity consumption of the system circuit is very large, the voltage regulation needs to be improved.
For reducing the influence of the conducting voltage drop on the system circuit terminal voltage, the conventional power supply needs an additional load detecting circuit. Since the load detecting circuit needs to cooperate with the output voltage detecting circuit, the circuitry layout of the power supply becomes complicated, and the volume and the cost of the power supply are both increased.
Furthermore, the power supply is further connected to the system circuit through two additional detecting wires such that the conventional output voltage detecting circuit can generate the detecting signal according to the system circuit terminal voltage. The uses of the additional detecting wires increase the fabricating cost. In addition, the additional detecting wires occupy much working space of the power supply and thus are not feasible to be used in some small-sized or portable power supply apparatuses.
There is a need of providing an output voltage detecting circuit so as to obviate the drawbacks encountered from the prior art.